A crane includes a hoisting winch for winching up and winching down a lift-object and a raising winch for raising and lowering a raising member such as a boom. The hoisting winch includes a drum around which a lifting rope which is a wire rope is wound. The hoisting winch causes to rotate the drum to wind up and wind out the lifting rope to winch up or winch down the lift-object. The raising winch includes a drum around which a raising rope, which is a wire rope, is wound. The raising winch causes to rotate the drum to wind up and wind out the raising rope to lift or lower the raising member. There is known a conventional information presentation system that presents information on the wire rope of the winch of the crane (see Patent Literature 1 listed below).
Patent Literature 1 discloses a system that detects the rotation amount of the drum of the hoisting winch of the crane, derives from the detected rotation amount the number of layers and the number of rows of the rope still wound around the drum, and displays the derived numbers of layers and rows of the rope on the display unit.
A load is applied to the wire rope wound out from the winch of the crane during a crane operation. For example, a load caused by a lift-object load is applied to the lifting rope, and a load caused by a forward moment of the raising member is applied to the raising rope. Therefore, fatigue accumulates due to the load applied to the wire rope, and the time comes when the wire rope needs to be replaced.
There has been proposed a system for presenting information on a rope of a winch of a crane, in which the numbers of layers and rows of the rope wound around the drum are displayed on the display unit as described above. However, there is no such system that presents information providing a guideline for determining the timing to replace a wire rope. Generally, it is simply determined that the timing to replace the wire rope has come when the elapsed time since mounting of a wire rope on a winch drum or the total operating time of a crane has reached a specific time period, or it is determined that the timing to replace has come by visually checking the overall condition of the wire rope and the condition of the wires constituting the wire rope.
In such general determining methods however, there is no guideline for determining the timing to replace a wire rope from a view point of fatigue accumulated in the wire rope related to the history of the load applied to the wire rope. Thus, there may be cases where a wire rope is replaced in an earlier timing than necessary, even though the actual accumulated fatigue is not yet so high as to replace the wire rope, which results in an increase in cost.